Rotary electric field fluid stirring apparatus



1954 M. F. JONES ROTARY ELECTRIC FIELD FLUID STIRRING APPARATUS Filed Aug. 14, 1952 2 Sheets-Sheet l NVENTOR F I 3 fl fazrce %Jones ATTORNEY Aug. 17, 1954 M. F. JONES 2,686,823

ROTARY ELECTRIC FIELD FLUID STIRRING APPARATUS Filed Aug. 14, 1952 2 Sheets-Sheet 2 FIG.2

l J J INVENTOR Maurce ;Jones ATTORNEY Patented Aug. 17, 1954 ROTARY ELECTRIC FIELD FLUID STIRRING APPARATUS Maurice F. Jones, Pittsburgh, Pa., assignor, by mesne assignments, to The Babcock & Wilcox Company, New York, N. Y., a corporation of New Jersey Application August 14, 1952, Serial No. 304,253

15 Claims.

This invention relates to fluid material stirring apparatus of the electric field type and, more particularly, to a novel stirring arrangement of this type in which the moving field is created by a rotatable inductor.

stirring of fluid materials in containers is frequently practiced for various reasons, such as to obtain uniform temperatures and unifcrm composition, to speed up reaction rates, and to control the direction of movement of the fluid material. For those materials which are electrically conductive, a moving electric field may be used to efiect the stirring. This has been accomplished hitherto by using inductor coils fixedly mounted relative to the container and energized with, for example, A. C. or pulsating D. C.

The inductor coils must be sufliciently long that the distance between magnetic poles of opposite polarity is greater than the minimum distance between a pole and the fluid material. otherwise, the magnetic flux path between opposite polarity poles will not pass, in any substantial strength, through the fluid material. This requirement necessitates relatively large and heavy fixed coils.

Where it is necessary or desirable to obtain a particularly oriented direction of movement of the fluid material, it has been proposed to use a plurality of successively energized coils with appropriate switching connections for conducting D. C. to the coils in a desired sequence. Thus, the created electric field in the fluid material moves along the line of the coils and in a direction determined by the sequence of energizing the coils.

For many materials, and particularly for those in containers of conductive material where the container itself will absorb a high proportion of the applied field, very heavy energizing currents for the stationary inductors are required. In D. C. pulse energized inductors, the handling of these heavy currents requires complicated and expensive switching connections, so that such arrangements have found only a limited use.

In linear motor field arrangements energized by A. C., a clumsy and relatively expensive construction is required, including a field-member which, of necessity, is large in order to provide the required long pole-pitch. With A. C. excitation, particularly of the polyphase type, a very low frequency source of energization is required in order that the speed of movement of the field Would not be too great. This has, in turn, required a special generator for producing the required very low frequency A. C., thus further increasing the cost of the arrangement.

Another complicating factor is introduced by the necessity for changing the power input to the inductors, under certain conditions, to change the force or velocity of the stirring motion. For example, in starting the stirring action a greater power input is required to overcome the inertia of the fluid material. If this greater power input is maintained after the fluid material has begun its movement, the stirring action may become sufficiently forceful to excessively stir the material and also erode the lining of the container, particularly when molten material is stirred in a refractory-lined container, thus introducing non-metallic inclusions of a harmful nature. Control of the intensity, directional pattern, or velocity of the stirring is desirable in pouring of material from the container. With stationary linear motors, such control of the moving field in the fluid material further complicates the switching equipment and further increases its cost.

In accordance with the present invention, a moving electric field, whose direction and inr tensity can be easily varied Without the necessity for expensive switching equipment, is provided in a novel manner. More particularly, an electric field device for stirring fluid material is provided in the form of a rotating inductor comprising a rotating fleld-magnet structure located in such proximity to the container for the fluid that the peripherally moving magnetic field, by its motion, induces eddy currents which draw the fluid material along in the direction of movement of the field, after the manner of an induction motor or an induction-disk motor. The field structure is continually supplied with magnetizing current through a current collector such as slip rings and associated brushes, and the magnitude of the current may be suitably varied by relatively inexpensive control devices.

The inductor may be rotated at a desired, preferably relatively low speed by means of an electric motor, with or without a speed change gearing, so that the speed of movement of the field may be simply and easily varied.

While the invention arrangement is applicable to the stirring of any electrically conductive fluid material in a supporting container, it is particularly useful for stirring molten metal in a ladle, furnace, or the like. Inductive stirring of the stationary inductor type has been used with molten metal containers for some time, such stirring being advantageous in reducng the temperature gradient in the molten metal body, for accelerating reactions. and for assuring a more uniform and homogeneous molten metal body.

The particular inductive stirring arrangement of the invention permits the use of a relatively deep ladle Whichis advantageous from the standpoint of having, for equal molten metal Capacity, less surface exposed for heat dissipation or oxidation, and requiring a lesser amount of slag for cover purposes thereby reducing the potentialities of changing the composition of the metal by reaction with the slag while the metal is in storage.

The bodies of molten metal frequently have a layer of slag on their top surfaces, both for protection from oxidation and/or for reaction with the molten metal. Whether or not the molten metal in a container is provided with a slag cover, the fluid body is generally termed a "bath" The aforementoned control of the intensty, rate of movement, and direction of the electric field is of particular importance when such a bath is electrically stirred. In starting the stirring action, more power is required than is needed to maintain the stirring action, due to the inertia of the molten material. Also, the stirring rate must he coordinated with the properties of the material, the geometry and material of the container, and the material with which the latter is lined. The stirring must he sufiicient to assure an acceptably low temperature gradient and homogeneous distribution of the constituents of the bathe, without being so forceful as to promote undesirable mixing of the slag cover into the molten metal, for example, or to erode the container lining.

Simple and easy control of the intensity and directional pattern of the stirring action is of great advantage when it is desired to pour the molten metal from one container into another, especially when lip pouring from a ladle into a casting mold. Among other things, it is frequently desirable to hold back the slag from the pouring lip in order to pour only the material into the receiving container. This may be efi'ected by so Choosing the intensity and directional pattern of the electric field that the circulation on the surface of the bath is away from the pouring lip, and of sufiicient intensity that the slag is efiectively held back from the pouring lip during pouring.

With the rotary inductor of the present invention, the speed of the field can be changed simply and easily by changing the angular velocty of the inductor. Also, the intensity of the field can be altered at will by simple switching arrangements controlling the fiow of energizing current to the inductor field structure.

While not limited thereto, the inductor of the present invention is particularly suited for use with the continuous casting arrargement shown and described in the copending application of I. Harter, Jr., Serial No. 304251, filed August 14, 1952. In such arrangement, ladle holding and pour stations are provided between the melting furnace and a continuous casting mold so that metal tapped from the furnaces may be stirred while being held for a pour, thus allowing efficient utilization of the melting furnace Capacity. Each holding or pour station comprises a cradle having the invention inductor mounted thereon and including supporting means for a ladle of molten metal.

For a better understanding of the invention 4 principles, reference is made to the following description of typical embodiments thereof as illustrated in the accompanying drawings. In the drawings:

Fig. 1 is a somewhat simplified and diagrammatic side View, partly in section, showing the invention as applied to an llustrative ladleurnace structure for a bath of molten steel or other hot molten electrically conducting material;

Fig. 2 is a similar view of the same structure, as seen from the front, or from the right-hand side of the apparatus shown in Fig. l; and

Fig. 3 is a simplified transverse sectional view, on a reduced scale, of the invention induction stirrer as applied to a relatively shallow melting urnace.

By way of example, the drawings illustrate the invention as applied to a pouring ladle l for molten metal removably supported in a suitable cradle on structure 5 provided With ,stationary trunnion supports providing an axis about which the supporting structure may be tilted to pour the contents of ladle The pouring axis preferably passes transversely through the pouring lip or spout H of ladle i, through which the contents of the ladle may be poured as described hereinafter. While ladle i is conventionally illustrated as being substantially rectangular in cross section, this is by Way of example only. In actual practice, and particularly in the handling of molten metals, the ladle would have a circular or elliptical cross section. such an arrangement involving a ladle removably supported in a tiltable Cradle is a feature of the above, mentioned co-pending application of I. Harter, Jr.

The ladle-element comprises a metal support structure l for a thick lining 8 of refractory material constituting the container for the fluid material, so as to adapt said container to hold a bath 9 of molten steel or other hot molten electrically conducting material.

Any suitable heat supply means may be used for supplying heat to a localized spot or Spots, or to localized portions of the bath. This is indicated diagrammatically in the drawings by pol 'phase arc electrodes lil playing arcs on the top or surface of the bath. The illustration of polyphase energized electrodes is exemplary only, and the heating may be effected by single phase arc elcetrodes or by other suitable heating means` This ladle l is provided with laterally extending trunnions I i coaxial with the tilting axis passing through pouring lip H, which are illustrated as being used for supporting the front portion of the ladle in the supporting cradle said trunnions fitting into upwardly opening notches !5 carried by the front frame-*nembers of the skeleton-type cradle 5. The rear bottom end of the ladle i rests on a rear cross-piece ll of the cradle-structure 5. Ordinarily, as a positive saieguard against relative motion between ladle i and cradle, suitable temporary looking-means (not shown) are used, for positively holding the ladle and the supporting- Cradle together, during the pouring operation, but if the pouring angle is not too great, the force of gravity may be regarded as a general indication of any suitable means for holding the ladle in its resting-position on the cradle.

The rear end of the ladle-supporting Cradle 5 is supported by resting on a foundation-member e, while the front end of the Cradle is provided with laterally extending trunnions 24,

which may or may not be coaxial with the ladletrunnions Hi, for supporting the front end of the cradle in the fixed or stationary supporting-brackets G. While the ladle trunnions M are shown, for Simplicity of illustration, as coaxial with the cradle trunnions 24, in actual practice the ladle trunnions would be located at or above the center of gravity of the ladle for con- Venience in handling the ladle by means of a crane or the like. The cradle can be tilted, so as to pivot on its trunnions 24, by any suitable means, such as a tilting-cable which lifts the rear end of the cradle-rame off of the founda tion-member 20.

The lower portions of the cradle-structure 5 are adapted to carry a rotatable field-member 30, and a small driving-motor Si therefor, both of which are shown as being disposed under'- neath the ladle-element 4.

Ladle 4 is formed with an inclined or orwardly and upwardly sloping bottom portion 32 forming an integral part of the ladle bottom 33, this ladle configuration forming part of the subject matter of the copending application of Maurice F. Jones, I. Harter, Jr., and Temple W. Ratcliffe, Serial No. 304252, filed August 14 1952.

The rotating field member or rotor inductor is supported immediately adjacent sloping bottom portion 32 so that the field of the induotor acts on the metal lying along this sloping bottom portion. The field thus operates to move the molten metal upwardly along portion 32, and this portion forms a transition section in the circulation path of the molten metal Whereby abrupt corners and abrupt changes in direction are eliminated thereby to reduoe the drag of the molten metal. Reversely acting elds, on either side of the field instantaneously acting on the bath, by virtue of the sloping portion 32, fall within the refractory lining and therefore have substantially no eifect on the bath 9.

The inclined bottom support portion 32 of the ladle-container 1, and preferably the entire bottom support member 33 of said ladle container, should be made of a material and Construction which minimizes the production of fieldclamping eddy-currents in said bottom support portion To this end, the portion 33 should be so constructed that it presents a high electrical resistance against the oirculation of eddy currents which are produced by the moving peripheral magnetic field of the rotating field-member 30, and it should also be of non-magnetic material, so as to not carry this magnetic field away, and thus prevent it from penetrating up into the bottom of the molten bath 9. To this end, the support member 33 of the ladle-container 'i is preferably made of stainless steel, or other nonmagnetic material, and is preferably given a high resistivity against the production and circulation of eddy Currents, by making it of a slotted, laminated or slatted Construction, so that it will exert the least possible damping on the magnetic field of the rotating field member 30. As shown, this portion 33 is made with parallel ront-to-rear-extending slats 34 of stainless steel, the slats being close enough together to properly support the refractory lining 8. The front and rear ends of the slats 34 are held together, or in position, by being supported by front and rear cross-pieces' and 3 5. If desired, the substantially horizontal portion of structure 33 may deliberately be made highly electrically and magnetically conductive to blank fields of inductor 30 from entering the rear portion of the bath 9 to prevent reversely acting fields efiecting upward or reverse flow toward the rear wall of the ladle.

The rotatable field-member 30 has a plurality or succession of peripherally disposed north (N) and south (S) magnetic poles 40, having a peripheral pole-pitch, from pole-center to polecenter, which is suihciently longer than the nearest distance between a peripheral pole-surface and the bath 9. so that a substantial portion of the magnetic field which fringes out from the poles d can eXtend out or penetrate into the bath. Since the field-member 30 is rotating, the magnetic field which penetrates into the bath is also moving, in the direction of rotation of the field-member.

It is this moving magnetic field, which penetrates into the bath, which causes the production of eddy Currents in the bath, these eddy currents in. turn reacting with the moving field to drag' themselves along with the field, and thus drag the bottom portion of the bath along with the field. The rotating field-member 30 is illustrated as being driven in a clockwise direction, as shown in Fig. 1, so that the moving field, in the bottom of the bath, moves toward the front of the iadle 4, thus setting up a flow-pattern li, in the bath, which not only stirs or circulates the molten material, but also continuously carries the top-surface portion of the nolten metal away from the spout i l thus tending to keep the spout free of becoming clogged with any surface-hoating slag (not shown), during the process of pouring, which will be subsequently described.

suitable exciting-means are provided, for elec trically exciting' or magnetizing the poles i of the r otating field-member 30. This exciting means is illustrated as including field-coils 45, slip-rings or other current-collector means 45, and an external eXciting-circuit which is illustrated as including a battery B and a field-rheostat &8. This field-rheostat 48 may be useful in making it possible, for brief times, as during the pouring-operation, to temporarily increase the eld-trength of the rotating field-member 39, beyond the strength corresponding to the con-- inuous rating of the field-coils 45, so that these fielcl-ooils 45 nay be temporarily overloaded, long enough to increase the eddy-current dragging efiect on the molten bath, thus producing a stronger stirring-motion which better keeps the surface-slag away from the pouring-spout i l during the pouring-operation. Also, the field strength can be decreased readily as conditions require.

In order to enable the moving magnetlc ,field to penetrate deeply enough into the bath 9, without clamping itself out, by reason of its own fast motion, it is necessary that the rotating fieldmember 30 shall be driven at a very low speed. The speed of rotation is also determined by the optimum desired rate of movement of the stirred material which, in turn, is conditioned upon selecting a stirring rate adequate to produce uni form temperature distribution and honogeneity of the bath without being so high as to cause erosion of the container lining or "dirtying" of the bath by causing any slag covering to admiri into molten metal, for example.

Considering these factors, the rotating field member will generally have a peripheral speed of from about to about 1500 feet per minute. If, for example, the diameter of induction stirrer 3@ is less than 12 feet, its speed may be stated to be 2,ese,823

from about 10 to about 150 R.. P. M. In a typical example, the rotating field-member 30 may have four poles and a diameter of about 38 inches, and be driven at a speed of 60 R. P. M., which speed may be increased or decreased as conditions may require. A four-pole field-member, at 60 R. P. M., produces a eyclic field Variation, at any relatively stationary point outside its periphery, at the rate of 2 cycles per second. Generall a field frequency of from 1 to` possibly 5 or 6 cycles per second will be usable with the the magnetic stirrer 36.

` The rotating field-member 30 is driven by the small motor 31, through any suitable speed-reduction means, such as a Cham-drive l, engaging a large sprocket-wheel 52 which is carried by the field-member 30. The motor 35 may be small, because it has to supply only enough power for the drag or pulling action on the molten bath, plus frictional losses, By way of example, the motor E! is illustrated as a variable-speed direct current motor, having a variable speed which may be controlled by a field rheostat 53 in circuit with its field-winding 54, as diagrammatically indicated in Fig. 1.

Since the rotating field-member 3@ is driven at such a low speed, and since a strong magnetic field is desirable, for Operating on the molten bath S, it is desirable to send relatively strong energizing-currents through the field-windings or eoils 45 of this field-member 53 3. Usually, therefore, these field-coils 45 will carry currents which produce such high heat-losses in the coils that the heat cannot be effectively dissipated by natural ventilation at the slow Operating-speed of the field-member 33. Hence, it is usually a necessary part of the invention to provide some sort of means, outside of the rotating field-member st, for supplying thereto a stream of air for cooling the field-coils 45.

As representative of a suitable ventilating means for this purpose, the inductor 3@ is illustrated as provided with the type of arrangement forming the subject matter of the copending application of Temple W. Ratclife, Serial No. 334254, filed August 14, 1952. In this 'arrangement, a fan Gli is mounted coaxially with the inductor 33 adjacent the right hand end thereof as seen in Fig. 2. This fan exhausts air out of the field-member 351, as indicated by the exhaustarrows si, thus drawing air axially through the field-member and cooling the field-coils l. The fan Bi] may be driven at any suitable or economical fan-speed, as by means of a small sprocketwheel. ?22, which is engaged by any suitable drivng-mechanism (not shown) Another novel structural-feature which is embodied in the rotating field-member 3%, not only because of its slow speed of rotation, but also because of its particular use underneath a ladle i for molten steel, consists of a thin non-ma& netic open-ended cylindrical metal shroud 65 which tightly peripherally surrounds the polepieces lil of the field-member 30. The thinness of the shroud prevents any material increase in the spacing between the rotating field-member 3% and the molten bath 9. The shroud is in good thermal contact with the peripheries of the poles so that it acts as heat-radiatng fins for coolthese poles. The shroud also acts as an airguiding means or air tunnel for facilitating the axia flow of cooling-air through the rotating field-member 39.

shroud 65 also prevents injury or clogging of field-member 30 by preventing tramp iron being drawn into the rotor, and by protecting the rotor from drippings of slag or metal from the ladle pouring lip when the ladle and its supporting cradle are tilted to pour the ladle contents. The shroud further presente a smooth surface for removal of extraneous material drawn toward or falling toward the rotor. For this reason, a non-magnetic scraper '66 is arranged in contact with shroud 65, and extending throughout the length thereof, so that such foreign material is scraped off the shroud while the inductor is rotated.

From the foregoing, it will be clear that, when the inductve stirrer or field-member se is associated with the ladle 4, it will maintain stirring of the molten metal during the time the latter is being held before pouring. The stirrer, moreover, permits the use of a much deeper ladle or bath with heat applied only to the top surface. Due to the stirring action, the molten metal is continuously moved past the heated portion of the bath where the arcing electrodes ill play an are on the bath surface. A deep bath has advantages over a shallow bath in that there is less heat less per unit Volume due to the iesser exposed upper surface, less oxidation for the same reason, and less robbing of constituents such as silicons etc. from the molten metal by the slag coating.

The stirring further promotes thorough and uniform mixing of the constituents of the molten il etal, preventing precipitation of any heavy elements or constituents of the alloy or bath mixture Thiis, a more homogeneous bath is provided.

When it is time to pour the molten metal, the whole arrangement, including cradle is tilted while the stirring is continued so that the bath is stirred during pouring. At this time, either the intensity of the field of inductor %8, or its speed of rotation, or both, may be increased to an extent sufcient to hold back the slag coating from the pouring lip during pouring. Thereby, substantially clean molten metal is poured from ladle 4.

While the preceding description of Figs. 1 and 2 is directed to the use of inductor or field-member 363 to stir molten metal in a holding or pouring operation, the inductor is not limited to such use and may be used with any type of molten metal furnace When it is desired to stir molten metal. Thus, in Fig. 3, inductor 39' is illustrated as applied to stir molten metal in a relatively shallow melting furnace "Ea, In this application, the lower wall or bottom of furnace lil, including lining 'li and preferably non-magnetic supporting metal oasing ?2, may be arched inwardly to form a semi-cylindrical recess or arch 15. The refractory lining 'H is built up on either side of arch l, as at l i, 'M to provide a uniformly sloping approach and exit from the arched section for the molten metal moved to the leit along the furnace bottom (as viewed in Fig. 3) so that a smooth flow path for the metal along the furnace bottom is provided between furnace side walls is, T. Due to the location of inductor 393' within arch ?5, the stirring field is concentrated in the bath overlying the arch and on either side thereof, so that two or more fields can be acting on the overlying metal in the same direction at the same time.

The invention thus provides a compact and practical induction stirrer for fluid material in which the speed and intensity of the magnetic field in the fluid material may be readily and simply varied without the use of complicated and expensive switching arrangements or special low frequency A. C. generators, such as are needed With stationary inductive stirrers of the linear field type. The power required t o rotate inductor 3& or 36' is very small, and the field energizing power is, in any event, substantially smaller than the overall power required for stationary inductors of equal efiect, when the switchboard losses of the latter are considered. The position of the inductor along te container surface to which it is adjacent may be easily adjusted for obtaining the optimum field pattern in the fluid material.

While a specific embodiment or" the invention has been shown and described in cletail to illustrate the application of the invention principles, it will be understood that the invention may be embodied otherwise without departing from such principles.

I claim:

l. An electric field device for stirring fluid material comprising, in combination, a container for the 'iuid material; a rotatable field member supported outside said container in closely spaced relation thereto and at a position where the uid material is adapted to be contained within the container; said field-member including a succession of peripherally disposed magnetic poles of opposite polarities having a peripheral pole pitch sufiiciently longer than the minimum distance from a peripheral pole face to the fluid material that a mo'ving magnetic field of substantial strength will penetrate the fluid material; and a cylindrical shroud, of non-magnetio material, surrounding said field member.

2. An electric field devioe for stirring fluid material comprising, in combination, a container for the fluid material; a rotatable field member supported outside said container in closely spaced relation thereto and at a position where the fluid material is adapted to be contained within the container; said field-member including a succession of peripherally disposed magnetic poles of opposite polarities having a peripheral pole pitch sufdciently longer than the minimum distance from a peripheral pole face to the fluid material i that a moving magnetic field of substantial strength will penetrate the fluid material; a cylindrical shroud, of non-magnetic material, surrounding said field member; and scraper means engaging the outer surface of said shroud.

3. An electric field device for stirring fluid material comprising, in combination, a container for the fluid material; a rotatable field member supported outside said container in closely spaced relation thereto and at a position where the fluid material is adapted to be contained within the container; said field-member including a successicn of peripherally disposed magnetic poles of opposite polarities having a peripheral pole pitch sufliciently longer than the minimum distance from a peripheral pole face to the fluid material that a moving magnetic field of substantial strength will penetrate the fluid material; a cylindrical shroud, of non-magnetic material, surrounding said field member; and means for supplying a stream of air through said shroud.

l. Handling means for a bath including hot molten electrically conductive material comprising, in combination, a container of relatively thicl; refractory material; a supporting shell embracing said container; heating means arranged to supply heat to a localized portion of the bath; and a rotatable field-member supported outside said container and shell adjacent the bottom Wall thereof and in closely spaced relation thereto;

said field-member having a succession of peripherally disposecl magnetic poles of opposite polarities having a peripheral pole pitch sufiiciently longer than the minimum distance from a peripheral pole face to the bath that a moving magnetic field of substantial strength will penetrate the bath; at least that portion of the shell penetrated by said field being of a Construction and material minimizing the production of fielddamping eddy currents in said shell portion.

5. The invention as defined in claim e characterized by variabie speed drive means for rotating said member at a relatively low speed.

6. The invention as defined in claim 4 characterized by exciting means for said poles and ineiuding field coils operatively associated with said poles, current collector means, a source of electric power, and adjustable control means controlling flow of power from said source to said field coils.

'1. The invention as defined in claim 4 characterized by exciting means for said poles and including field coils operatively associated with said poles, current collector means, a source of electric power, and adjustable control means controlling flow of power from said source to said field coils; and means for supplying a stream of air to cool said field coils.

8. The invention as defined in claim 4 characterized by a cylindrical shroud, of non-magnetic material, surrounding said field-member.

9. The invention as deflned in claim 4 characterized by a cylindrical shroud, of non-magnetic material, surrounding said field-member; and scraper means engagng the outer surface of said shroucl.

19. The invention as defined in claim 4 characterized by a cylindrical shroud, of non-magnetic material, surrounding said field-member; and means or supplying a stream of air through said shroud.

11. Handling means for a bath including hot molten electrically conductive material comprising, in combination, a container of relatively thick refractory material having at least a portion of its bottom wall inclined upwardly; a supporting shell embracing said container; heating means arranged to supply heat to the free surface of the bath; and a rotatable field-member supported outside said container and shell adjacent said inclinecl bottom wall portion and in closely spaced relation thereto; said field-member having a succession of peripherally disposed magnetic poles of opposite polarities having a peripheral pole pitch sufflciently longer than the minimum distance from a peripheral pole face to the bath that a moving magnetic field of substantial strength will penetrate the bath.

12. Handling means or a bath including hot molten electrically conductive material comprising, in eombination, a ladle of relatively thick refractory material formed with a pouring lip; a supporting shell embracing said ladle; a supporting structure removably receiving said ladle; supporting said structure for tiitng about an axis passing transversely through the ladle pouring lip to pour material from the ladle; heating means on said structure arranged to supply heat to the free surface or" the bath; and a rotatable field member supported on said structure outside said container and shell adjacent the bottom wall thereof and in closely spaced relation thereto; field-member having a succession of peripherally disposed magnetic poles of opposite polarities having a peripheral pole pitch sufficiently longer than the minimum distance from a peripheral pole face to the bath that a moving magnetic field of substantial strength Will penetrate the bath; at least that portion of the shell penetrated by said field being of a Construction and material minimizing the production of field damping eddy currents in said shell portion.

13. An inductive stirrer comprising a rotatable field-member, said field-member having a succession of periphe'ally disposed magnetic poles of opposite polarities; a cylindrical shroud, of non-magnetic material, surrounding said fieldmember; and variable speed drive means for rotating said field-member at a relatively low speed.

14. An inductive stirrer comprising a rotatable field-member, said field-member having a succession of peripherally disposed magnetc poles of opposite polarities; a cylindrical shroud, of non-magnetic material, surrounding said fieldmember; variable speed drive means for rotating said field-member at a relatively low speed; and scraper means engaging the outer surface of said shroud.

15. An inductive stirrer comprising a rotatable References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,068,558 Bally July 29, 1915 1,884,637 Feehan Oct. 25, 1932 2,339,964 Tama Jan. 25, 1944 FOREIGN PATENTS Number Country Date 999.012 France Sept. 26, 1951 

